The invention concerns adhesive and sealant systems.
Adhesive and sealant systems are known from Ullmanns Enzyklopädie der technischen Chemie, 4th Edition, Volume 14, page 227 (1997).
They consist of high-polymeric substances having as good strength as possible. Most adhesives and sealants contain high-molecular-weight organic substances as the basic raw materials or reactive organic compounds which are precursors of polymeric substances and which react during the adhesive and sealing process to form polymers.
It is known that for various adhesive and sealant systems, based for example on epoxy resin, polyurethane resin or vinyl ester resin, hydrophobic, pyrogenic silicas are very effective thixotropic agents in comparison to hydrophilic, pyrogenic silicas. Moreover, such adhesive and sealant systems can be made more stable in storage with hydrophobic, pyrogenic silicas than with hydrophilic, pyrogenic silicas (Degussa Schriftenreihe Pigmente (2001) No. 27 and No. 54).
Owing to their fine-particle character, known pyrogenic silicas give rise, to increased dust formation and a long incorporation or wetting time in liquid systems.
It is also known (Degussa Schriftenreihe Pigmente No. 63, 2001, page 25) that due to compaction, pyrogenic hydrophilic silica can be incorporated into the binder in a shorter incorporation time, using a high-speed mixer or high-speed planetary mixer for example.
The incorporation time is understood to be the time during incorporation in which the fine-particle silica has completely disappeared from the surface of the binder and is wetted with the binder. Depending on the batch size, dispersing unit and formulation, the incorporation time can last for up to several hours and in many applications it is therefore the speed-determining step for the preparation of the product.
Compacting the silica reduces the formation of dust by the silica. The lower volume of the compacted silica can also be advantageous in the design of dispersing units.
Disadvantageously, in most applications the viscosity of the binder containing pyrogenic silica decreases markedly during compaction as the compacted bulk density of the pyrogenic silica increases. In the same way the dispersibility of the silica deteriorates during compaction as the compacted bulk density increases. This is manifested for example in the form of speck formation and greater surface roughness. Both effects are significant disadvantages. For that reason the use of compacted hydrophilic, pyrogenic silica in adhesives and sealants is relatively limited.
The object is therefore to produce adhesive and sealant systems in which the above disadvantages do not occur.